As Clinton builds a delegate lead with overwhelming support from Democratic Party insiders, Sanders' supporters challenge a presidential nominating process they describe as rigged in her favor. But party rules that give superdelegates power to lift up the establishment's choice — even if he or she struggles in primaries and caucuses — were put in place much earlier, in 1982.

Their design was to give party leaders and elected officials more of a say on top-of-the-ticket candidates after big general election losses by George McGovern in 1972 and Jimmy Carter in 1980.

And even in a 2016 year of anti-establishment politics, a change to superdelegates' freedom to support whichever candidate they want isn't likely to happen anytime soon.

"We wanted to temper the influence of interest group leaders and party activists in the nominating process," said Al From, staff director for the House Democratic Caucus in the 1980s, which pushed for creation of superdelegates. "So if it looked like what you're now seeing on the Republican side, with renegade candidates like Donald Trump whom the party doesn't like, these people would be a counterbalance."

"But the truth is, Democratic superdelegates haven't had any influence in turning around a nomination," he said.

Currently, Clinton has a 91-65 delegate lead over Sanders based on results from primaries and caucuses. But when superdelegates are added, Clinton's lead widens substantially over Sanders, the self-described democratic socialist, to 548-87, including two new endorsements she received Tuesday, according to the AP count. It takes 2,383 delegates to win. Many of those superdelegates, including those in New Hampshire, endorsed Clinton late last year and said in a recent AP survey they weren't changing their minds even after Sanders' big win there.

"It's fundamentally undemocratic to have a superdelegate system that gives so much power to party elites," said Charles Chamberlain, executive director for Democracy for America. His grass-roots group is circulating petitions urging superdelegates to follow the will of voters. "It's ridiculous we have to go through this every eight years, just to make sure superdelegates do the right thing."

There are currently 714 Democratic superdelegates, about 30 percent of the delegates needed to clinch the nomination. They are members of Congress, governors, party officials and members of the Democratic National Committee who automatically attend the national convention and can support the candidate of their choice. The Republicans have some automatic delegates but not nearly as many.

Before superdelegates, these Democratic insiders typically had to run against grass-roots constituents in the primary and caucus process to become a delegate. Many opted not to, keeping them off the convention floor when Sen. Edward M. Kennedy staged a spirited challenge to Carter for the nomination at the 1980 Democratic National Convention that left the party deeply divided.

"The idea was to make two classes of people, including superdelegates," said Elaine Kamarck, author of "Primary Politics" and a superdelegate who has already endorsed Clinton. "It would be for situations if there were some kind of inconclusive result from the primaries, they could exercise their own judgment."

Only twice before did superdelegates come close to overruling the rank and file.

In 1984, they overwhelmingly supported Mondale over Hart's insurgent campaign, lifting Mondale to the number needed to win before the national convention after he failed to win a majority of delegates from primaries and caucuses. But Mondale had a plurality of delegates and had also won more primary votes. In any event, Mondale went on to lose 49 states to Ronald Reagan in the general election, the worst Electoral College defeat ever for a Democrat.

In 2008, Clinton's early lobbying gave her a 2-to-1 superdelegate advantage over Illinois Sen. Barack Obama before primary and caucus voting began. But as Obama racked up caucus and primary wins, his supporters assailed the superdelegate process as unfair. He eventually won over the uncommitted and flipped Clinton votes, securing a majority of both pledged and superdelegates.

Obama's successful general election prompted the DNC in 2010 at his prodding to re-examine superdelegates' influence. A special commission recommended that superdelegates be required to vote based on results from their state's primary or caucus. But the DNC decided to keep superdelegate authority intact and instead reduce their numbers; a rules committee member said it couldn't embrace the proposal because DNC members would never agree to strip their voting power. Superdelegates now make up 15 percent of the total delegates, down from 20 percent.

"As long as the DNC is in charge of the process and the rules and they are superdelegates themselves, you really need a revolution to change that," said From, co-founder of the now-defunct Democratic Leadership Council.

The Sanders campaign, acknowledging an uphill fight, says the primaries and caucuses are far from over.

"The process is what the process is," said Tad Devine, a senior adviser to Sanders who actually helped craft the superdelegate rules in the 1980s. He says the aim of the rules was always intended to "come behind a candidate chosen by voters," with the campaign planning to make a broader pitch to superdelegates later in the primary season.

"We believe superdelegates will take their role and responsibility in this process very seriously," Devine said, "making a judgment on who can best succeed in the general election after the voters have spoken — not before."